Manufacturing process of semiconductor devices include a step of polishing an object made of elemental silicon (e.g., polysilicon, single crystalline silicon, or amorphous silicon), silicon compounds, metals or the like. In this step, when a semiconductor to be manufactured includes a gate electrode made of polysilicon and a silicon-based material other than polysilicon surrounding the gate electrode, such a silicon-base material other than polysilicon, which may be silicon nitride or silicon dioxide, is required to be polished preferentially. For instance, Patent Literature 1 proposes a polishing liquid capable of polishing a layer containing a silicon material other than polysilicon quickly and limiting the polishing of polysilicon. The polishing liquid proposed contains colloidal particles, organic acid, and at least one nonionic additive selected from nonionic surfactant and nonionic hydrophilic resin. Such a polishing liquid, however, does not have good washing efficiency because it contains nonionic additive and the nonionic additive remains after the polishing. Therefore this polishing liquid does not satisfy user's demand fully.